The best way I found to get the "cold calls" to stop from the duct guys and others like them is as follows. "Oh, my (father or son depends on your age) is your biggest competitor in this area and he'd be thrilled to know about your promotions! So you do understand why I'll never use your services..." And as simple as that they have never called back...
Years ago I'd say "Oh, my father is your biggest competitor in this area and he'd kill me if I used you guys!!!! So you do understand why I can never use your services..."
It's funny when they start naming other local business asking "is it _____ he owns?"